1. Field of the Invention
The present invention relates to an organic light emitting diode (OLED) display device, and, more particularly, to the OLED display device and a method for sensing characteristic parameters of pixel driving circuits, which are capable of correcting non-uniformity of luminance through simple and rapid sensing of the characteristic parameters.
2. Discussion of the Related Art
An active matrix organic light emitting diode (AMOLED) display device is a self-luminous device in which an organic light emitting layer emits light through re-combination of electrons and holes. Since the AMOLED display device exhibits high luminance, and employs a low driving voltage while having an ultra-slim structure, it is expected to be a next-generation display device.
Such an AMOLED display device includes a plurality of pixels, each of which includes an organic light emitting diode (OLED) constituted by an anode, a cathode, and an organic light emitting layer interposed between the anode and the cathode, and a pixel driving circuit for independently driving the OLED. The pixel driving circuit mainly includes a switching thin film transistor (hereinafter, referred to as a “TFT”), a capacitor, and a driving TFT. The switching TFT charges the capacitor with a voltage corresponding to a data signal in response to a scan pulse. The driving TFT controls the amount of current supplied to the OLED in accordance with the level of the voltage charged in the capacitor, to adjust the amount of light emitted from the OLED. The amount of light emitted from the OLED is proportional to the amount of current supplied from the driving TFT to the OLED.
In such an AMOLED display device, however, TFT characteristics such as driving TFT threshold voltage Vth and process tolerance factors (e.g., mobility, parasitic capacitance, and channel width/length) are non-uniform among pixels due to process tolerances. For this reason, non-uniformity of luminance may occur in the AMOLED display device. To solve this problem, a data compensation method is employed. In accordance with this data compensation method, the characteristic parameters of the driving TFT in each pixel driving circuit are measured, and input data is adjusted, based on the result of the sensing.
The characteristics of the driving TFT may be measured through sensing of amounts of current flowing through the corresponding pixel at different voltages. For an AMOLED display device having an increased size, however, it is more difficult to rapidly measure amounts of current flowing through a number of pixels. For example, U.S. Pat. No. 7,834,825 discloses a method for sensing an amount of current flowing through a power line (a VDD or VSS line) of an OLED panel while turning on pixels one by one. However, this method has a problem in that there is a difficulty in achieving rapid sensing because the current sensing time is delayed due to parasitic capacitors present in parallel on the power line to achieve increased resolution.
Furthermore, in conventional cases, the system for sensing the characteristics of the driving TFT is complex. For this reason, after shipment, it is difficult to measure and compensate the characteristics of the driving TFT.